Fuel cells provide clean and efficient mechanisms for energy production. However, both enzymatic and microbial biofuel cells are typically bulky devices containing three-dimensional voluminous fuel reservoirs and macro-scaled electrodes of different geometries. Accordingly, there remains a need for small, portable, lightweight fuel cell-based systems.
Enzyme-based fuel cells run on the same fuel as the human body, such as the glucose in Coca-Cola, but without the expense of the noble metal catalysts of conventional fuel cells, or the short shelf-life of microbial fuel cells. The design of enzymatic fuel cells today is based on over 20 years of research focused on ensuring that each liberated electron is efficiently and rapidly transferred to a solid electrode, either via electron-carrying mediators, or via direct electron transfer from enzyme to electrode. Although electron transfer is no longer a performance limiter, enzyme fuel cells remain limited in power output and lifetime, and thus are ill-suited to power practical devices such as cell phones and autonomous sensors.
The gist of the present challenge is to design cells that allow rapid transport of both fuel and oxygen to bound enzyme, and thereby circumvent the rate-limited performance of current designs. More specifically, cells must be designed to ensure an ever-present three-phase-interface between fuel, air and enzyme, a condition which is essential for each enzyme to turn over at its maximum rate.